None.
The present invention relates to centrifugal blood pumps.
Delicate surgical procedures require that the site of surgery remain motionless. This requirement made early heart surgery difficult to impossible as interruption of the heart""s pumping action for the required length of surgical time would invariably be fatal.
Traditional heart surgery is carried out with the aid of devices generally referred to as a xe2x80x9cheart/lung machinexe2x80x9d. With the heart/lung machine in operation, the patient""s heart can be stopped while the surgeon performs the delicate surgery required to repair the ailing heart. The two fundamental parts of the heart/lung machine are a blood pump that takes the place of the arrested heart, and an oxygenator that replaces the patient""s lungs during the surgical procedure. The heart/lung machine also includes filters, blood reservoirs, and plastic tubing as required to connect several parts of the bypass circuit.
Although the mortality and morbidity of heart/lung bypass surgery have been greatly reduced, hospital stays of two weeks and a gradual recovery of over six months are the norm. Many of the bad side-effects of heart/lung surgery are thought to be the result of blood contact with the various parts of the heart/lung machine.
Quite recently, a new technique for heart surgery has been developed. The technique is generally referred to as xe2x80x9csurgery on the beating heartxe2x80x9d. In this process, a stabilizing device is used to hold steady the portion of the heart that is being addressed by the surgeon. The heart/lung machine is not required, because the heart and lungs function normally throughout the procedure. Advantages claimed for this method include reduced hospital stay, reduced hospital cost, and fewer side-effects such as mental deficit. All of these advantages are claimed due to the reduced blood trauma by elimination of blood contact with the devices making up the heart/lung machine.
Beating-heart surgery is not without some problems both for the surgeon and the patient. First, the most commonly used stabilizing device consists in part of a series of small suction cups that attach to the portion of the heart being stabilized. The relatively high vacuum required to grasp the heart typically results in blood blisters on the heart muscle at the site of the suction cups. Second, since the heart is pumping, the surgeon must contend with blood spurting from the coronary artery during graft attachment. Third, there is no data concerning the durability of the coronary artery graft done with this procedure. Lastly, the cost of disposable devices is comparable to that required for conventional open-heart surgery.
The single component of the heart/lung machine that is most suspect for blood trauma is the oxygenator. This is typically a device with hundreds of hollow plastic fibers. The blood passes over the outside surface of the fibers and oxygen passes through the fibers to imitate the function of the natural lungs. Unlike the natural lungs, however, the hollow fibers are made out of a plastic material and must have a large surface area in order to oxygenate the blood and remove carbon dioxide from it. Elimination of the oxygenator would also eliminate tubing, reservoirs, and filters resulting in a significant reduction of foreign blood-contact surfaces.
The mammalian heart performs two pumping functions. The first function is to pump blood through the lungs, and the second is to pump blood to the remainder of the body. The elimination of the oxygenator can be accomplished through the use of two mechanical blood pumps to duplicate the function of the natural heart. This method has been tried experimentally but has not gained favor because of several problems. First, the use of two blood pumps requires that they be synchronized. This is technically difficult with roller-type pumps, which are the most commonly used type in open-heart surgery. Second, cannulae must be placed in both the systemic and pulmonary circuits, which increases surgical time. Third, the extra cannulae crowd the operating area and compromise ready access to the heart. Fourth, although conventional centrifugal blood pumps readily self-synchronize, their size adds to the crowding of the operating field.
With the present invention, the reduction of blood trauma is achieved by eliminating the oxygenator. The present device is a two-chambered centrifugal blood pump. The first chamber has a first inlet and a first outlet and the second chamber has a second inlet and a second outlet. A shaft extends through and between the first and second chambers and defines a rotational axis. First and second impellers are also positioned within the first and second pumping chambers, respectively. In the preferred embodiment, one chamber pumps deoxygenated blood to the natural lungs, and the other chamber pumps oxygenated blood to the remainder of the body.